1. Field of the Invention
The present invention relates to a drive controller that controls a pointer used in an instrument such as a vehicle speedometer, a tachometer, or any other instrument.
2. Description of the Related Art
In paragraph “0021” of JP-A-H09(1997)-145742, it is described that “a sweeping operation can be performed without generating the pulsation of a pointer without performing a detailed step operation, a sweeping operation not causing a driver to feel discomfort can be acquired, and the marketability and the designability of a cross coil-type instrument can be improved”. In addition, in paragraph “0003”, it is described that “by performing a sweeping operation in which, after the ignition switch is turned on, the pointer of a cross coil-type instrument such as a speedometer, a tachometer, or the like is operated in a full scale from the initial state and then is returned to the initial state, the sweeping operation is considered to improve the marketability and the designability”, and, in paragraph “0004”, it is described that “when a sweeping operation is performed depending on driving torque supplied from the above-described driving processing unit operating a cross coil-type instrument at a normal time, the driving torque is high, and thus, the pointer overshoots for an instructed electric angle (stepping operation), and there is a problem in that the pulsation is generated in the operation of the pointer so as to cause the driver to feel discomfort”.
In vehicle instruments of recent years, stepping motors are used instead of the cross coil that is described above. A stepping motor used in a vehicle instrument requires torque higher than dynamic friction torque of a constant-speed period at the time of performing a sweeping operation so as to satisfy the acceleration, the resistance against vibration, and the like of the pointer in a normal operation.
The period of a sweeping operation is configured by an acceleration period, a deceleration period, and a constant-speed period. In a case where a motor is driven with the same torque as that at the time of performing a normal operation during the constant-speed period of the sweeping operation, the smoothness is degraded due to excessive torque, and the pulsation may be easily generated in the operation of the pointer, whereby the driver is caused to feel discomfort. In addition, in a case where a motor is driven at a speed near its vibration resonance point (resonance frequency) in the constant-speed period, the pulsation tends to be more remarkable.